This frequency divider by 10 uses discrete components only. Modern equivalent components can be used as the circuit is from an 80's documentation. Nearby frequencies can be used.
This simple lie detector was found in Popular Electronics. Transistors are commonly used. The...
This one-transistor alarm can be used with much more sensors than the two shown by the figure....
This circuit was obtained in a 1975 documentation. The maximum frequency depends on the diodes and the...